Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device having an improved cathode electrode structure and heightened electron beam focusing efficiency, and an electron emission display device with the electron emission device.
Description of Related Art
Depending upon the kinds of electron sources, electron emission elements can be classified into those using hot cathodes or those using cold cathodes.
There are several types of cold cathode electron emission elements including a field emitter array (FEA) type, a surface-conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
To construct an electron emission display device, an array of the electron emission elements is formed on a first substrate to make an electron emission device, and the electron emission device is combined with a second substrate having a light emission unit including a phosphor layer, a black layer, and an anode electrode.
In a common FEA-type electron emission display device, electron emission regions are formed on a first substrate, and cathode and gate electrodes are provided for respective sub-pixels as driving electrodes for controlling the emission of electrons from the electron emission regions. A phosphor layer, a black layer, and an anode electrode for accelerating the electron beams are formed on a surface of a second substrate facing the first substrate.
The electron emission regions are electrically connected to the cathode electrodes to receive electric currents required for the electron emission. The gate electrodes are placed on a plane different from the cathode electrodes, and an insulating layer is interposed between the gate electrodes and the cathode electrodes. For instance, the gate electrodes may be placed over the cathode electrodes in an insulating manner. Openings are formed at the gate electrodes and the insulating layer to expose the electron emission regions.
When predetermined driving voltages are applied to the cathode and gate electrodes, an electric field is formed around the electron emission regions at the sub-pixels where the voltage difference between the two electrodes exceeds a threshold value, and electrons are emitted from those electron emission regions. The emitted electrons are attracted by a high voltage applied to the anode electrode, and directed toward the second substrate to collide with the phosphors at the relevant sub-pixels and to emit light.
However, with the above-described light emission structure, the electric field is not uniformly focused over the entire area of an electron emission region. That is, the electric field is mainly focused on the upper periphery of the electron emission region facing a gate electrode, and electrons are emitted therefrom. The emitted electrons are spread toward the second substrate with random inclination angles, and land on the correct color phosphors of the corresponding sub-pixels as well as on the incorrect color phosphors at the sub-pixels neighboring thereto, thereby deteriorating the screen color purity.
Furthermore, with the operation of the electron emission display device, non-stable driving voltages are applied to the cathode electrodes, or non-stable voltage drops are made at the cathode electrodes, so that the electron emission regions at the respective sub-pixels may receive different driving voltages. In this case, the emission characteristics of the electron emission regions become non-uniform, and the light emission uniformity of the respective sub-pixels is deteriorated.